import java.text.DecimalFormat;
import java.util.Scanner;


public class P1004 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		Scanner in=new Scanner(System.in);
		float balance=0;
		int i=12;
		while(i>0){
			balance+=in.nextFloat();
			i--;
		}
		DecimalFormat df = new DecimalFormat(".00");
		float result=balance/12;
		System.out.println("$"+df.format(result));
	}

}
